1. Field of the Invention
The present invention relates to a system and method for generating an enhanced acoustic transmission signal for a psychoacoustically-motivated auditory band communication channel carrying data and audio signals.
2. Discussion of the Related Art
When exploring the psychology of hearing as a means to improved human computer interfaces, it becomes apparent that there are vast differences between the human auditory system and acoustical transducers used by computers. Though both convert sound pressure waves into energy differentials, the resultant signals do not have similar spectral content. A transducer, (e.g., a microphone) often has a near-flat frequency response that is not tuned to human speech. It converts all frequencies into appropriate voltage levels that are limited only by its sensitivity and dynamic range. If digitally sampled for computer enhancement, the frequency response is additionally determined by the Nyquist frequency. In the digital domain, there exists many methods for extracting all of the frequencies present in the signal whether or not they are audible by human ears. A very different signal is made available through the auditory system for human cognition. For the human percept, there are many preprocessing mechanisms that limit access to the frequencies in the environment. These preprocessing mechanisms include the natural resonance of the ear canal, the time-varying non-linear transfer function of the middle ear, and the complex conversion of mechanical pressures to electrochemical firings taking place in the cochlea. The physics of this complex conversion process is quite remarkable—sound energy is converted into mechanical motion, which is converted back to sound energy, then converted back into mechanical motion, which is detected and converted into electrochemical nerve signals. These processes selectively enhance perception of human speech and important localization phenomenon, as opposed to simply converting sound pressure into neuron firings. The human auditory system distinguishes sounds on the basis of duration, direction, pitch, loudness, and timbre.
Psychoacoustic masking has been used in digital speech processing over the last 10 years. There also exists masking techniques used in the encoding of audio signals to best avoid perceptual encoding noises. Additionally, there are masking techniques used in some acoustic noise reduction schemes for reducing the aggressiveness of the reduction. However, there are currently no viable psychoacoustic masking applications for use in in-band communication channels for creating enhanced acoustic transmission signals that are compatible with legacy analog communication systems, such as conventional telephones.